Skip to main content
U.S. flag

An official website of the United States government

Measuring wood specific gravity, correctly


G. Bruce Williamson



Publication type:

Miscellaneous Publication

Primary Station(s):

Forest Products Laboratory


American journal of botany. Vol. 97, no. 3 (2010): p. 519-524.


The specific gravity (SG) of wood is a measure of the amount of structural material a tree species allocates to support and strength. In recent years, wood specific gravity, traditionally a forester’s variable, has become the domain of ecologists exploring the universality of plant functional traits and conservationists estimating global carbon stocks. While these developments have expanded our knowledge and sample of woods, the methodologies employed to measure wood SG have not received as much scrutiny as SG’s ecological importance. Here, we reiterate some of the basic principles and methods for measuring the SG of wood to clarify past practices of foresters and ecologists and to identify some of the prominent errors in recent studies and their consequences. In particular, we identify errors in (1) extracting wood samples that are not representative of tree wood, (2) differentiating wood specific gravity from wood density, (3) drying wood samples at temperatures below 100 °C and the resulting moisture content complications, and (4) improperly measuring wood volumes. In addition, we introduce a new experimental technique, using applied calculus, for estimating SG when the form of radial variation is known, a method that significantly reduces the effort required to sample a tree’s wood.


Williamson, G. Bruce; Wiemann, Michael C. 2010. Measuring wood specific gravity... correctly. American journal of botany. Vol. 97, no. 3 (2010): p. 519-524.


Publication Notes

  • We recommend that you also print this page and attach it to the printout of the article, to retain the full citation information.
  • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.